The increased number of cars, especially in urban areas are causing an increase of exhausts, with health and environmental problems connected thereto. The harmful components causing the major problems are mainly carbon oxide, hydro carbons and nitrogen oxides. The underlaying cause for the unclean exhausts are incomplete combustion. Different techniques are used for reducing the amounts of these components, the most common is the wellknown catalytic technique, which provides a combustion of the exhausts outside the actual combustion process .
Concerning diesel exhaust gases there are a number of problems to solve. One of these is the soot formation, another is the nitrogen oxides formed during the combustion. It is possible to reduce the emissions of carbon oxide and hydro carbons using a catalytic equipment. The complications occuring doing this is, besides oxidizing CO and HC to CO.sub.2 and water, that a certain amount of nitrogen is oxidized to nitrogen oxide (NOx). The reason for this is that a diesel engine inevitably is working with a surplus of air. Another problem is that the soot after a certain time hinders the function of the catalyzer. The soot can be reduced by for example partly or completely substituting diesel with ethanol. The problems with the nitrogen oxides however remains.